The present invention relates to a missle seeker system and particularly to a missle seeker optical system which will extend the effective look angle of the missile seeker objective.
The smaller the look angle, the smaller the acquisition envelope. In other words, with a look angle of only 90.degree. the pilot must point the aircraft to acquire a target. When the missile seeker look angle is increased up to 135.degree. off-boresight, pointing of the aircraft is not so critical and target acquisition is greatly enhanced.
Missile technology has progressed to the point where a gimbal arrangement allows the missile objective to cover a range larger then a hemisphere. Accordingly, a portion of the nose of the missile behind the hemispherical nose dome has been made transparent to take advantage of this greater flexibility. It has been found, however, that the different optical parameters encountered by the radiation passing through the non-spherical portion of the window, would, in some cases, be so distorted as to be practically worthless.
According to the present invention an optical correction system is provided for dome astigmatism with a minimum number of optical surfaces which may be easily fabricated. This optical system uses a wedge angle in the conical portion of the dome to provide some of the optical correction. The forward end of the conical portion has a thickness identical to the spherical section and the inner and outer surfaces of the conical portion are tangent to the inner and outer surfaces respectively of the spherical portion. This results in a very good quality image with a minimum number of optical surfaces. With the addition of two corrector lenses on the gimbal fork the image seen through the conical portion of the dome is of a quality nearly identical to that seen through the spherical portion of the dome.